1. Field of the Invention
The present invention relates to a wiring layout on an auxiliary wiring package that only includes wiring lines and external pads, and also relates to a printed circuit wiring board.
2. Description of the Related Art
Recently, the density of BGA (Ball Grid Array), CSP (Chip Scale Package), etc., mounted on a semiconductor integrated circuit has significantly increased in accordance with the demand for multiple pins (signal lines) and for reducing the size of the circuit. Thus, wiring on the printed circuit wiring board is crowded making it difficult to place wiring between plural locations in a prescribed area. To resolve the above-mentioned problem, a auxiliary wiring package capable of temporary bypassing and drawing out wiring lines has been proposed by the present applicant as described in Japanese Patent application Laid Open No. 11-68026.
Further, because the circuit board has been advanced since the time of filing the Japanese Patent application (i.e., 1998), mass production thereof is performed using a built-up construction method. However, this example increase the total cost for a printed circuit wiring board. Further, placing wiring between plural locations on the printed circuit wiring board is still difficult using the above-noted built-up technology.
In addition, planning a wiring layout using a wiring auxiliary package is more complex than planning a conventional wiring layout.
Further, according to the above-mentioned technology, to easily draw wiring from external pads located at a center of the package and to partially reduce the density of wiring at a predetermined location, a auxiliary wiring package including only wiring lines and external pads (i.e., excluding a semiconductor integrated circuit) is oppositely arranged to an electronic part (IC) attached below the printed circuit wiring board. A plurality of through holes are also formed at predetermined positions through the wiring board that correspond to external pad lines formed at a center of a multiple pin package of the electronic part. External pad lines are also formed at the center and outside sections of the auxiliary package, so that the wiring between the outside and central external pad lines are drawn within the auxiliary wiring package. However, a wiring layout using the auxiliary package is not specifically addressed, and the total cost for the printed circuit wiring board increases.